With present technology for miniaturizing electronic circuitry, a high density of electronic circuits and components can be located on a printed circuit board (PCB). Accordingly, electrical connectors are needed to electrically and mechanically interconnect a first PCB, such as a back panel or mother board, to a second PCB, such as a daughter board. It is typically necessary for such connectors to have a high signal capacity. That is, the connector should pass a high number of signals per unit volume of the connector. However, closely spaced electrical signals can interfere with one another. This interference is referred to as "cross talk." Controlling such cross talk is especially important in high density connectors such as high pin count (HPC) connectors.
One method for controlling cross talk is to connect certain terminals in a high density connector to conductive areas of a printed circuit board that are in turn grounded. This solution is provided externally to the connector. In addition, there are a variety of connector arrangements for minimizing such cross talk within the connector itself.
For example, U.S. Pat. Nos. 4,655,518, 4,686,607, and 4,869,677 disclose a daughter board/backplane assembly with contact elements dedicated for grounding purposes. Header contact elements have contacts that can be connected to ground or a predetermined potential on a backplane. The header contact elements have other spring contacts carried by an inside header wall for touching contacts carried by a right angle receptacle outer wall. Other contacts are integral with and perpendicular to the contacts carried by the right angle receptacle outer wall for connection to the daughter board.
U.S. Pat. No. 5,228,864, Jul. 20, 1993, titled "Connectors With Ground Structure," discloses a high density electrical connector assembly with means for controlling impedance and cross talk within the connector. This patent is incorporated by reference herein and is briefly summarized below, as is another patent, namely, U.S. Pat. No. 5,104,329. The drawings of these two patents may advantageously be referred to when reading the following summaries, in which the reference numerals in parentheses refer to the elements depicted in the drawings.
The assembly disclosed in U.S. Pat. No. 5,228,864 includes a high density vertical connector or receptacle (ref. no. 500) interconnecting a circuit assembly and a mating connector. The vertical receptacle comprises an insulative housing (ref. no. 528), a plurality of "first conductive electrical contact elements" (ref. no. 535) mounted in the housing, a pair of external conductors (ref. no. 240), and an insulative spacer (ref. no. 590). The insulative housing has a first mating surface (ref. no. 548), side walls (ref. no. 530), and a plurality of passages (ref. no. 584) within the second side walls and arranged in rows and columns extending from the first mating surface through the housing. The housing also includes means for aligning the housing with the external conductors. The conductive electrical contact elements (535) are described as having any configuration (i.e., male elements, female elements or gender neutral) so long as they are useable as vertical contact elements. In addition, each of the external conductors (240) has at a plurality of "fifth contacts" (ref. no. 265) and a plurality of "sixth contacts" (ref. no. 275), wherein the fifth contacts are on one of the side walls (530) for contacting the side contacts on a side wall of a mating connector. The patent discloses that each of the external conductors can be an elongated shield member with a bent end portion for extending into corresponding retaining grooves or slots (ref. no. 552) in the mating surface of the connector.
U.S. Pat. No. 5,104,329, Apr. 14, 1992, titled "Electrical Connector Assembly," discloses an electrical connector assembly (ref. no. 10) including a receptacle member (ref. no. 12) and a pin header (ref. no. 60). The receptacle member has a housing including an inner body portion (ref. no. 22) and two opposed outer side walls (ref. no. 24), which together define elongate cavities (ref. no. 36). A plurality of "first contact terminal members" (ref. no. 40) are disposed in the inner body portion and a plurality of "second contact terminal members" (ref. no. 46) are disposed in the elongate cavities. The pin header includes a housing member (ref. no. 62) with a plurality of "third electrical contact terminal members" (ref. no. 78) and a ground bus member (ref. no. 90) disposed continuously along a side of the pin header housing. The ground bus member is adapted to be received in one of the elongate cavities of the receptacle and electrically engage the second terminal members when the receptacle member and pin header are mated.
One problem with prior art connectors of the type discussed above is that they do not provide for stage mating between corresponding contact terminals of the pin header and receptacle. For example, with reference to U.S. Pat. No. 5,104,329, the ground bus member on the pin header makes contact simultaneously with all of the second contact terminal members. There is no provision, e.g., for grounding one or more receptacle terminals prior to connecting other receptacle terminals to corresponding terminals of the pin header. Moreover, the use of a continuous ground bus of the type disclosed by U.S. Pat. No. 5,104,329 precludes the use of the surface area occupied by the ground bus for other purposes, such as the provision of additional contact terminals. Such additional contact terminals would be extremely useful in providing enhanced signal carrying capacity to the connector assembly.